Method of recording images within a furnace using a thermal imaging camera comprising a borescope

ABSTRACT

A method of recording images within a furnace using a thermal imaging camera comprising a bore scope connected to a digital camera unit is described, comprising the steps of: (a) inserting the borescope into the interior of the furnace, (b) collecting one of more images of the interior of the furnace using the thermal imaging camera with the borescope at a first position, and (c) moving the borescope from the first position to a second position and collecting one or more images of the interior of the furnace as the borescope is moved from the first position to the second position, wherein the borescope movement is guided by means of a guide device comprising a movable borescope mounting, mounted externally on the furnace.

The present invention relates to a method for recording thermal imagesof the interior of a furnace and apparatus therefor.

Steam methane reformers are examples of furnaces in which the furnacecontains a plurality of externally-heated, catalyst-filled tubes. Areaction mixture containing methane and steam is passed through thetubes over a steam reforming catalyst disposed within the tubes togenerate a gas mixture containing hydrogen, carbon monoxide and carbondioxide, often termed synthesis gas. The external heating is typicallyprovided by a combustion gas produced by combustion of a fuel using aplurality of burners arranged on the internal walls of the furnace.

Efficient operation of furnaces, including steam methane reformers, isof growing importance and mal-operation, for example resulting in hotspots, can lead to damage to the furnace, the tubes and the catalyst.Therefore, there is a need for operators to better understand theconditions within the furnace and in particular the temperatures ofsurfaces, including the tube wall temperatures, and how these might becontrolled to improve efficiency in the utilization of the fuel andprevent damage to the furnace, the tubes and the catalyst.

U.S. Pat. No. 8,300,880 discloses a method for determining temperatureinformation on a plurality of tubes in a furnace by capturing aplurality of digital images of the interior of the furnace andprocessing the images to obtain temperature information for theplurality of tubes.

U.S. Pat. No. 8,219,247 discloses a method of operating a furnace havingprocess tubes and multiple burners where it is desired to conform thetemperatures of the process tubes to selected target temperaturecriterion. The method uses a plurality of images comprising pixel dataassociated with the tubes to obtain temperature information that is usedto adjust burner flow rates to result in desired tube wall temperatures,for example to minimize the temperature deviation between tube walltemperatures at a predetermined elevation in the furnace.

US20170171418 discloses a method for thermal imaging of an interiorspace of a high temperature furnace through an opening in a wall of thefurnace. An outer housing houses at least a portion of an air-cooledrigid borescope. A camera is operatively connected to the cooledborescope but is located such that it is isolated from the air passingthrough the outer housing.

These methods use portable thermal imaging cameras to collect thedigital images. Portable thermal imaging cameras are manually operatedand are used to collect images by typically directing a borescopeconnected to a digital camera unit through an inspection-hole in thefurnace wall. The thermal imaging camera captures time-varyingtemperature data within a furnace in the form of a thermal ‘video’, i.e.as a sequence of images, each containing temperature data at an instantin time. For furnace temperature monitoring the use of a portablethermal imager offers significant advantages over a point pyrometer,allowing large amounts of data to be captured very rapidly.

However, a number of challenges remain. The field of view of the thermalimaging camera is typically much smaller than the total field of viewthrough an inspection port, so its position and orientation within thepeephole must be varied to maximise data capture. This movement of theimager compromises the quality of the data by introducing motion blurand parallax effects, complicating analysis. A problem with usingportable thermal imaging cameras therefore is that the ability ofcomputer software used to process the images to determine thetemperatures within the furnace is reduced by variability introduced bythe manual collection method. There is therefore a need to reduce thevariability in image collection using portable thermal imaging cameras.Moreover, using portable thermal imaging cameras to capture images withthe most useful field of view requires skilled, specially-trainedoperators and there is a need to allow broader use of such equipment ina more reproducible way.

Accordingly the invention provides a method of recording images within afurnace using a thermal imaging camera comprising a borescope connectedto a digital camera unit, comprising the steps of: (a) inserting theborescope into the interior of the furnace, (b) collecting one of moreimages of the interior of the furnace using the thermal imaging camerawith the borescope at a first position, and (c) moving the borescopefrom the first position to a second position and collecting one or moreimages of the interior of the furnace as the borescope is moved from thefirst position to the second position, wherein the borescope movement isguided by means of a guide device comprising a movable borescopemounting, mounted externally on the furnace.

The invention further provides an apparatus for recording images withina furnace, comprising (i) a thermal imaging camera comprising a digitalcamera unit connected to a borescope and capable of recording aplurality of images, and (ii) a guide device comprising a movableborescope mounting for guiding the borescope, wherein the guide deviceis configured to be mounted externally on the furnace and to guide themovement of the borescope from a first position to a second positionwithin the furnace.

The invention further provides a furnace comprising the apparatus, saidfurnace having one or more inspection holes or other orifices throughwhich the borescope is inserted.

The invention further provides a guide device suitable for guiding aborescope of a thermal imaging camera within a furnace, said guidedevice comprising a borescope guide device comprising a movableborescope mounting and configured to be mounted on the exterior of thefurnace.

By “mounted” we include the options of the guide device fixedpermanently in place on the exterior of the furnace or fixed temporarilyand moved from location to location when desired.

The present invention includes inserting the borescope of a thermalimaging camera through an opening in a wall of a furnace and thencollecting one or more images of the interior of the furnace. Thethermal imaging camera comprises a digital camera unit connected to theborescope. The borescope is typically an elongate tube or housing havinga viewing end and a sensor end aligned along the same longitudinal axis.The thermal imaging camera desirably comprises a digital cameracomprising an optical sensor; a rigid borescope comprising an elongatedhousing having a viewing end and a sensor end, and a multi-element relaylens assembly within the elongated housing having at least two opticalpieces for directing a real image viewed by the rigid borescope to thedigital camera. The viewing end of the borescope suitably comprises alens and the sensor end of the borescope is operatively connected to thecamera. The digital camera may be rigidly-attached to the sensor end ofthe borescope. The thermal imaging camera may further comprise a batteryor power-source connection, a controller, and a display. Such thermalimaging cameras are commercially available, e.g. from AMTEK® LandInstruments.

In order to protect the lenses in the borescope from damage and toimprove image quality, it may be desirable to cool the borescope, forexample by means of a cooling fluid cool gas passing through a housingthat encloses at least part of the borescope. Thus, in a preferredarrangement, the thermal imaging camera comprises an outer housingcontaining at least a portion of the rigid borescope extending from theviewing end of the borescope and extending towards the sensor end, theouter housing having an outlet at the viewing end and an inlet adjacentthe sensor end to permit a cooling fluid, such as air, to be passedthrough the housing. A partition member may be present within the outerhousing to prevent the cooling fluid entering the camera. Such a thermalimaging camera is described in the aforesaid US2017/0171418, which isherein incorporated by reference.

The one or more images are collected at the first position, which may beany suitable position for the collection of the one or more images, suchas a position at which the borescope is directed towards a surfacewithin the furnace. The surface within the furnace may be any surfaceabout which temperature information is wanted. The method is ofparticular use in establishing the temperature profiles of tubes withinthe furnace, especially catalyst-filled tubes within the furnace.

The furnace may be a steam reformer comprising a plurality of tubescontaining a steam reforming catalyst. The furnace typically has one ormore inspection holes or other suitable orifices or openings throughwhich the borescope may be inserted.

The present invention requires that the borescope is guided, by means ofa guide device comprising a movable borescope mounting, from the firstposition to the second position, and that a plurality of images iscollected as the borescope is moved from the first position to thesecond position. The guide device controls the movement of the borescopewithin the furnace in a pre-determined manner. The second position maybe any suitable position for the collection of images and includes aposition adjacent to or overlapping with, the first position. Thus, theborescope may be moved from the first position to a distinct secondposition or may be moved in a single stage or in a combination of stagesin a circuitous or serpentine path from the first position to the secondposition, which may be adjacent to, or overlap with, the first position.

By collecting the plurality of images in a controlled manner, errors inthe generation of thermal data are reduced and a more complete image ofthe interior of the furnace is realised. Furthermore, computer softwareis more readily is able to combine the images for determining overalltemperatures of the surfaces in the furnace. Thus, the method mayfurther comprise a step of (d) combining the images collected in steps(b) and (c) to create a composite image of the interior of the furnace.The composite image may be used for the identification of surfaces ofinterest within the furnace. The combining of the images may beperformed by processing the images using commercial computer softwaresuitable for image manipulation. Using the collected images, it ispossible to extract temperature data on the surfaces of interest eitherdirectly from the composite image or by reference back to thecorresponding points in the original images.

By using the guide device comprising a movable borescope mounting, thequality of the information from the thermal imaging camera is improved.The movement from the first position to the second position may bemanual or driven by a motor. However, for periodic measurement usingportable equipment, manual movement of the camera and borescope arepreferred as this reduces complexity and cost. By using the guidedevice, the thermal imaging measurement is more reproducible because theguide device may be mounted in the same manner at each orifice throughwhich the borescope is inserted and the movement of the borescope simplyrepeated for each collection of images. Therefore, the processing ofeach of the combinations of collected images to produce an overallcomposite image of the interior of the furnace may be considerablysimplified and improved.

The guide device comprises a movable mounting. The movable mountingenables the borescope to be moved in the desired manner. The moveablemounting preferably constrains the movement of the borescope to a singledegree of freedom such that the tip of the borescope moves from thefirst position to the second position along a continuous path. This pathmay include straight line segments, circular or elliptical arcs,segments of arbitrary continuous curves, or a combination of these.

The movable mounting may be located within a frame configured to bemounted on the exterior of the furnace. The movable mounting may belocated within the frame by any manner that enables the desiredcontrolled movement, such by means of hinges, a ball-and-socket joint,or within a track. If within a track, the movable mounting may bemounted on bearings or a plurality of wheels.

Preferably, the movable mounting is configured to be rotated. Wherelocated in a frame, this may be achieved by providing the movablemounting with wheels or bearings that engage with a circular trackdisposed within the frame.

The borescope may be attached to the guide device or may be insertedthrough an opening in the guide device that accommodates the housing ofthe borescope. The borescope may, if desired, be secured to the guidedevice by a clamp or locking pins on the outside of the housing thathold it in place. The guide device may be mounted on the external wallof the furnace and then the borescope inserted through the movablemounting and into the furnace. Alternatively, the borescope may beinserted through the movable mounting and the combination of guidedevice, borescope and thermal imaging camera moved from location tolocation around the furnace.

The borescope typically will provide a conical field of view around anoptical axis aligned with, and extending from, the end of the borescope.In one embodiment, the end of the borescope is moved in a curve. Thecurve described by the end of the borescope as it moves from the firstposition to the second position may be chosen such that the compositefield of view captured during the movement is maximised. In a preferredembodiment, the movable mounting holds the borescope at an angle ofbetween 20 and 90 degrees, preferably at an angle of between 25 and 75degrees, to a surface of the furnace on which the guide device ismounted. This allows the borescope to capture images of surfaces in thefurnace that may not readily be observed otherwise. In a particularlypreferred embodiment, the movable mounting holds the borescope at anangle of between 25 and 75 degrees to the furnace and provides acircular movement from the first position to the second position,thereby causing the borescope to describe a cone within the furnace asthe borescope is moved from the first position to the second position.

The guide device may comprise a frame in the form of a shaped metal orceramic plate supporting the movable mounting. The frame may have lobesor horns supporting spacing members or pins extending from the back ofthe frame that act to space the frame from the wall of the furnace onwhich it is to be mounted.

The frame may further comprise one or more clamps, such as a screwclamp, for clamping the guide device to a wall of a furnace.Alternatively, or additionally, one or more magnets may be placed on thefurnace-facing side of the frame to assist in securing its position onthe exterior of the furnace. The frame may also be attached to thefurnace by means of spring clips or other suitable attachment means.Brackets on the exterior of the furnace may also be used to support orattach the frame or guide device. Adjustable spacing means may beprovided to hold the frame rigidly on uneven furnace walls. The framemay also comprise a supporting member that extends from the bottom ofthe frame in use towards the furnace to rest on the bottom edge of theopening through which the borescope is inserted. Alternatively, oradditionally, the guide device may be supported on a stand comprisingone, two or more legs connected to the frame, which desirably areadjustable to support the weight of the guide device and thermal imagingcamera apparatus. This improves the stability and rigidity of theapparatus during the collection of the images. The use of a stand allowsthe guide device to be mounted externally to the furnace withoutaffixing it to the exterior wall of the furnace where this is notpossible.

The frame may further comprise a scale indicating the distance themovable borescope mounting has moved during the collection of images.The movable borescope mounting may then comprise means to indicate theposition of the movable mounting relative to the scale.

A circular track may be fixed within the frame that provides a circularspace in which the movable mounting may be located. Other shapes oftrack may be used. The movable mounting may then move on the trackwithin the frame. Where a circular track is present, the movablemounting may be a lobed structure, e.g. a 3-, 4- or 5-lobed structurecomprising freely rotating wheels mounted in each of the lobes that runon the track and enable the movable mounting to rotate within the frame.The movable mounting may also comprise a circular plate mounted onbearings within a circular track or may be any other design in which themovable mounting may be rotated. A smooth circular movement is mostpreferred to maximise the quality of the collected images and simplifythe processing of the collected images.

The movable mounting desirably further comprises a borescope mounting,which may be tubular, that passes through the movable mounting. Theborescope mounting may be positioned anywhere suitable on the movablemounting. Where the movable mounting is a lobed structure comprisingfreely rotating wheels mounted in each of the lobes, the borescopemounting may be positioned on a line between two of the wheels, andequidistant between the wheels. The longitudinal axis of the borescopemounting may, where the guide device is mounted parallel to the wall ofthe furnace, be at an angle of between 20 and 90 degrees, preferably atan angle of between 25 and 75 degrees to the frame. Where the frame isparallel to the wall of the furnace the angles to the wall of thefurnace will be the same. The borescope mounting desirably has adiameter large enough to enable insertion of a borescope through thetube. A fixing collar may be present on the borescope mounting to lockthe borescope in place.

One or more handles may be mounted on the frame to assist withpositioning of the guide device on the furnace wall before and duringits use.

The guide device should be suitably sized to hold the thermal imagingcamera. The guide device may have a width in the range of about 0.1 to0.9 metres or 0.3 to 0.9 metres. If mounted on a stand, the stand mayhave a height in the range of about 1.0-2.5 metres, preferably about 1.5to 2.0 metres.

In use, the guide device is mounted onto the exterior wall of thefurnace over a suitable orifice or opening, such as an inspection port.Where present, the clamp and/or magnets may be used to attach the guidedevice to the wall. The spacing means, stand, legs and support member,where present, help to hold the apparatus in the desired position. Athermal imaging camera comprising a borescope and a digital camera unitis coupled to the guide device. The borescope is inserted into theinterior of the furnace and held in place by the guide device. One ormore images are recorded using the thermal imaging camera at a firstposition. The borescope connected to the thermal imaging camera is thenmoved in a controlled manner, by means of the guide device, from thefirst position to a second position, which may be adjacent to or overlapwith the first position. During the movement from the first position tothe second position, the thermal imaging camera records multipleadditional images in the interior of the furnace. The image recorded atthe first position may be combined with the multiple images recorded asthe borescope is moved to create a composite image of the interior ofthe furnace, from which temperature data for surfaces of interest may beobtained.

Assuming steady furnace operation, each image shows a part of the samesource object. The change in position and orientation of the borescopebetween successive images can be inferred using any suitable method,allowing for the known distortion introduced by the camera optics andtaking advantage of the constraints on movement imposed by the guide.Once the position and orientation of the borescope in each frame isknown, the frames may be merged to create a composite image.

The invention will further be described by reference to the followingdrawings in which:

FIG. 1 is a side-view depiction of a guided thermal imaging camera inuse in a tubular furnace;

FIG. 2 is a plan drawing of one embodiment of a guide device;

FIG. 3 is a side drawing of the thermal imaging guide device of FIG. 3 ;

FIG. 4 is an oblique depiction of a further embodiment of a of a guidedevice;

FIG. 5 is an oblique depiction of a further embodiment of a guide devicesimilar to that in FIGS. 2 and 3 with a thermal imaging camera attached;

FIG. 6 is a front view of a further embodiment of a guide device with athermal imaging camera attached; and

FIG. 7 is a back view of the embodiment of FIG. 6 ;

In FIG. 1 , a thermal imaging camera, comprising a rigid borescope 10attached to a digital camera unit 12, is inserted through an inspectionport 14 into the interior of a furnace. The inspection port 14 isbounded by the furnace wall 16, which is protected by an internalrefractory layer 18. The furnace may be a steam reformer furnacecomprising multiple rows of tubes 20 containing steam reformingcatalyst. The rows of tubes are heated by a plurality of burners mountedon the interior of the furnace wall (not shown). The thermal imagingcamera is mounted in a guide device comprising a frame 22 supporting amovable mounting 24. The frame is mounted on the exterior of the wall 16by meant of spacing pins 26. The movable mounting 24 is configured to berotated in the frame 22 about an axis of rotation 28 thereby moving theborescope in a circular path from a first position to a second positionadjacent to or overlapping with the first position. The borescope 10 isattached to the movable mounting 24 at an angle of about 45 degrees tothe wall 16 of the furnace. The circular movement of the mounting 24from the first position to the second position therefore causes theborescope 10 to describe a cone 30 as it is moved from the firstposition to the second position. Arrows are included to depict therotation of the borescope 10 and camera unit 12. As a result of usingthe guide device, the field of view 32 of the borescope 10 moves in acontrolled manner within the steam reformer furnace, that enhances thecapture of thermal image data.

In FIGS. 2, 3 and 4 a guide device is depicted comprising a frame 22 inthe form of a shaped metal plate supporting a movable mounting 24. Theframe comprises upper left and right horns 42, 44, each supporting aspacing pin 26 extending from the back of the frame. Beneath the horns,the frame comprises a circular track 44, fixed centrally within theframe, that provides a circular space in which the movable mounting 24is located. The diameter of the circular track 44 is about 30 cm.Beneath the track 44, the frame further comprises a clamp portion 46extending vertically downwards that comprises a screw clamping device 48for clamping the guide device to an exterior wall of a furnace. Themovable mounting is a four-lobed structure comprising freely rotatingwheels (FIG. 4, 54 ) mounted in each of the lobes that run on the track44 and enable the movable mounting to rotate within the frame. Themovable mounting further comprises a tubular borescope mounting 50 thatpasses through the movable mounting. The borescope mounting 50 ispositioned on a line between two of the wheels, and equidistant betweenthe wheels. The longitudinal axis of the borescope mounting 50 is at anangle of about 45 degrees to the frame. The borescope mounting 50 has adiameter large enough to enable insertion of a borescope therethrough. Afixing collar 52 is present on the borescope mounting 50 to lock theborescope in place. In FIG. 4 , a handle 60 is mounted between the horns40, 42, to assist with positioning of the guide device on the furnacewall before and during its use.

FIG. 5 depicts apparatus comprising a thermal imaging camera comprisinga borescope 10 and a camera unit 12 attached to a guide device similarto that in FIGS. 2 and 3 in which the borescope 10 is inserted throughthe borescope mounting 50.

In FIGS. 6 and 7 a guide device is depicted comprising a frame 22 in theform of a shaped metal plate supporting a movable mounting 24. The framehas upper left and right horns 42, 44, each supporting magnet blocks(FIG. 7, 80 ) extending from the back of the frame. Beneath the horns,the frame comprises a circular track 44, fixed centrally within theframe, that provides a circular space in which the movable mounting 24is located. Beneath the track 44, the frame further comprises a supportmember (FIG. 7, 84 ) extending perpendicular to the frame 22 forsupporting the apparatus on the edge of an opening in the furnace wall.The movable mounting is a lobed structure comprising freely rotatingwheels mounted in each of the lobes that run on the track 44 and enablethe movable mounting to rotate within the circular track 44 within theframe 22. The movable mounting further comprises a tubular borescopemounting (FIG. 6, 50 ) that passes through the movable mounting 24. Theborescope mounting 50 is positioned on a line between two of the wheels,and equidistant between the wheels. The longitudinal axis of theborescope mounting 50 is at an angle of about 45 degrees to the frame.The borescope mounting 50 has a diameter large enough to enableinsertion of a borescope 10 therethrough. A fixing collar (FIG. 6, 52 )is present on the borescope mounting 50 to lock the borescope in place.The entire device is supported on two legs 70 that extend downwardlyfrom the sides of the frame 22. The track 44 further comprises a scale72 that indicates by means of a pointer 74 attached to the movable guide24, the degree of rotation of the borescope 10. The viewing end of theborescope comprises a lens 90 through which the images may be capturesduring use.

In use, the guide device is mounted onto the exterior wall of thefurnace over a suitable orifice such as an inspection port. The clamp 48or magnets 80 are used to attach the guide device to the wall and helpto hold it in the desired position. A thermal imaging camera comprisinga borescope 10 and a digital camera unit 12 is attached to the guidedevice by inserting the borescope 10 through the borescope mounting 50into the interior of the furnace and fixing it in place using the collar52. One or more images are recorded using the thermal imaging camera ata first position. The movable mounting 24 is then rotated manuallywithin the frame 22 causing the camera 12 and borescope 10 to rotatefrom the first position to a second position, which may be adjacent toor overlap with the first position. The angle at which the borescope ismounted results in the borescope describing a cone as the mounting 24 isrotated from the first position to the second position. During therotation, the thermal imaging camera records multiple additional imagesof the interior of the furnace.

The image recorded at the first position is combined with the multipleimages recorded as the borescope and attached camera are rotated tocreate a composite image of the interior of the furnace, from whichtemperature data for the tube surfaces may be obtained.

For the embodiments of the guide devices shown in FIGS. 1-7 , all theimages share a common fixed point, and each image is an approximaterotation of the previous image about this point.

The invention claimed is:
 1. A method of recording images within afurnace using a thermal imaging camera comprising a borescope connectedto a digital camera unit, the furnace having an interior, the methodcomprising: (a) inserting the borescope into the interior of thefurnace, (b) collecting one of more images of the interior of thefurnace using the thermal imaging camera with the borescope at a firstposition, and (c) moving the borescope from the first position to asecond position and collecting one or more images of the interior of thefurnace as the borescope is moved from the first position to the secondposition, wherein borescope movement is guided by means of a guidedevice comprising a movable borescope mounting, mounted externally onthe furnace, wherein the movable borescope mounting provides a circularmovement from the first position to the second position, thereby causingthe borescope to describe a cone within the furnace as the borescope ismoved from the first position to the second position.
 2. The methodaccording to claim 1 further comprising a step of (d) combining theimages collected in steps (b) and (c) to create a composite image of theinterior of the furnace.
 3. The method according to claim 1 wherein themovement of the thermal imaging camera from the first position to thesecond position is manual or driven by a motor.
 4. The method accordingto claim 1 wherein the movable borescope mounting holds the borescope atan angle of between 25 and 75 degrees, to a surface of the furnace onwhich the guide device is mounted.
 5. The method according to claim 1wherein the borescope is inserted through the movable borescope mountingand into the furnace, the movable borescope mounting holds the borescopeat an angle of between 25 and 75 degrees to a surface of the furnace onwhich the guide device is mounted and provides a circular movement fromthe first position to the second position, thereby causing the borescopeto describe a cone within the furnace as the borescope is moved from thefirst position to the second position.
 6. The method according to claim1 wherein the furnace is a steam reformer comprising a plurality oftubes containing a steam reforming catalyst.
 7. An apparatus forrecording images within a furnace, comprising (i) a thermal imagingcamera comprising a digital camera unit connected to a borescope andcapable of recording a plurality of images, and (ii) a guide devicecomprising a movable borescope mounting for guiding the borescope,wherein the guide device is configured to be mounted externally on thefurnace and to guide movement of the borescope from a first position toa second position within the furnace and wherein the movable borescopemounting provides a circular movement from the first position to thesecond position, thereby causing the borescope to describe a cone withinthe furnace as the borescope is moved from the first position to thesecond position.
 8. The apparatus according to claim 7 wherein thethermal imaging camera comprises a camera comprising an optical sensorand a rigid borescope comprising an elongated housing having a viewingend and a sensor end, a multi-element relay lens assembly within theelongated housing having at least two optical pieces for directing areal image viewed by the rigid borescope to the camera, the viewing endcomprising a lens, wherein the sensor end of the rigid borescope isoperatively connected to the camera.
 9. The apparatus according to claim8 wherein the thermal imaging camera comprises an outer housingcontaining at least a portion of the rigid borescope extending from theviewing end of the borescope and extending towards the sensor end, theouter housing having an outlet at the viewing end of the rigid borescopeand an inlet adjacent the sensor end to permit a cooling gas to bepassed through the outer housing.
 10. The apparatus according to claim 7wherein the movable borescope mounting is configured to be rotated. 11.The apparatus according to claim 10 wherein the movable borescopemounting is located within a frame and comprises wheels or bearings thatengage with a circular track disposed within the frame.
 12. Theapparatus according to claim 10 wherein the movable borescope mountingis configured to hold the borescope at an angle of between 25 and 75degrees to a to a surface of the furnace on which the guide device is tobe mounted.
 13. The apparatus according to claim 7 wherein the movableborescope mounting has an orifice through which the borescope isinserted, the movable borescope mounting is configured to hold theborescope at an angle of between 25 and 75 degrees to a surface of thefurnace on which the guide device is mounted and provide a circularmovement from the first position to the second position, thereby causingthe borescope to describe a cone within the furnace as the borescope ismoved from the first position to the second position.
 14. A furnacecomprising the apparatus according to claim 7, said furnace having oneor more inspection holes or other orifices through which the borescopeis inserted.
 15. The furnace according to claim 14 wherein the furnaceis a steam reformer containing a plurality of catalyst-filled tubes. 16.A device suitable for guiding a borescope of a thermal imaging camerawithin a furnace, said device comprising a borescope guide devicecomprising a movable borescope mounting and configured to be mounted onthe exterior of the furnace wherein the movable borescope mountingprovides a circular movement from a first position to a second position,thereby causing the borescope to describe a cone within the furnace asthe borescope is moved from the first position to the second position.17. The device according to claim 16 wherein the movable borescopemounting is configured to be rotated.
 18. The guide device according toclaim 17 wherein the movable borescope mounting is located within aframe and comprises wheels or bearings that engage with a circular trackdisposed within the frame.
 19. The device according to claim 16 whereinthe movable borescope mounting is configured to hold the borescope at anangle of between 25 and 75 degrees to a surface of the furnace on whichthe device is to be mounted.
 20. The device according to claim 16wherein the movable borescope mounting has an orifice configured to holdthe borescope, the movable mounting is configured to hold the borescopeat an angle of between 25 and 75 degrees to a surface of the furnace onwhich the guide device is to be mounted and provide a circular movementfrom the first position to the second position, thereby causing theborescope to describe a cone within the furnace as the borescope ismoved from the first position to the second position.